This report describes an interrelated study of the oxidation products formed in asphalt during the processing of road mixes and aging in the road and the interactions of asphalt and its oxidation products with aggregate to form the asphalt-aggregate adhesive bond. A method for the qualitative and quantitative determination of ketones, car- boxylic acids, dicarboxylic anhydrides, and 2-quionolone types in asphalts was developed and applied to ten penetration-grade asphalts recovered from 11- to 13-year-old pavements. Carbonyl types strongly adsorbed on the aggregate surface were quantitatively determined. Independent studies identified ketones & dicarboxylic anhydrides as significant carbonyl-type oxidation products in aspahlts. Evidence for the structural types of ketones and anhydrides in asphalts is given. Esters were not found in the asphalt oxidation products. Mineral surfaces and components naturally present in asphalt were both found to catalyze the oxidation of aspahlt. Asphalt-aggregate interactions were studied by microcalorimetry which gave evidence of multilayer adsorption of asphalt molecules in the asphalt-aggretate interphase region. Further evidence for the orientation of molecules in the interphase region was provided through photomicroscopic studies. The significance of the work to asphalt paving technology is discussed. /FHWA/

Supplemental Notes:

Work was carried out in a government interagency cooperative research program. Contract Manager: J.A. Zenewitz, HRS-23.